Understanding the molecular signaling in programmed cell death is vital to a practical understanding of inflammation and immune cell function. Here we identify a previously unrecognized mechanism that functions to downregulate the necrosome, a central signaling complex involved in inflammation and necroptosis. We show that RipK1 associates with RipK3 in an early necrosome, independent of RipK3 phosphorylation and MLKL-induced necroptotic death. We find that formation of the early necrosome activates K48-ubiquitin-dependent proteasomal degradation of RipK1, Caspase-8, and other necrosomal proteins. Our results reveal that the E3-ubiquitin ligase Triad3a promotes this negative feedback loop independently of typical RipK1 ubiquitin editing enzymes, cIAPs, A20, or CYLD. Finally, we show that Triad3a-dependent necrosomal degradation limits necroptosis and production of inflammatory cytokines. These results reveal a new mechanism of shutting off necrosome signaling and may pave the way to new strategies for therapeutic manipulation of inflammatory responses.
Alturki, Norah A.; McComb, Scott; Ariana, Ardeshir; Rijal, Dikchha; Korneluk, Robert G.; Sun, Shao-Cong; Alnemri, Emad S; and Sad, Subash, "Triad3a induces the degradation of early necrosome to limit RipK1-dependent cytokine production and necroptosis." (2018). Department of Biochemistry and Molecular Biology Faculty Papers. Paper 133.
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